This invention relates to a water bottom dredging apparatus, and more particularly to a dredging apparatus for removing sludge, ooze and the like on the water bottom with high sludge concentration, without causing turbulence of sludge in water, by use of a combination of a specific suction head and a pump unit.
Recently, accumulation of sludge or muddy refuse of various kinds, including refuse from living life and industrial waste, has advanced seriously in the estuaries, water and sea ports, lakes, swamps, etc., and the necessity for removing such sludge has become acute. Under such circumstances, attempts are being made widely for improving the living environment by dredging the embayments, lakes, marshes and so forth. There is generally employed for such dredging a method in which the suction head of a pump is set at a place to be dredged to pump out sludge at such place and pumped-out sludge is transferred along with water to the other place, and in such method is used a dredging machine having a construction suited for the area to be dredge. A typical example of such dredging machines is disclosed in Japanese Patent Laid-Open No. 28741/1972. The dredging machine shown in this Japanese Patent is constituted essentially from a pump, a suction pipe adapted to said pump, an end-spread suction head secured to the end of said pipe and arranged movable underwater, and a plurality of screw augers mounted at the end of said suction head. This machine has an excellent dredging performance and allows efficient removal of sludge, but it still leaves room for further improvements for performing effective dredging and transfer of sludge. Generally it is required in this type of dredging machines that the dredging operation can be accomplished without disturbing sludge to keep water in the dredged region non-turbid, that the area where disturbance of water current is caused in the dredged region is minimized, that sludge can be pumped out with high concentration, that the gas produced from sludge during the dredging operation can be recovered, that there is no "leftover" of sludge, and that even coarse or large-sized debris can be removed out. The dredging machine of the above-cited Japanese patent does not fulfill these requirements to a satisfactory degree. That is, this dredging machine can not meet all of these requirements and is low in dredging efficiency and also unable to perform smooth transfer of sludge water by a pump. When the sludge concentration in the sludge water is too low, too much time and energy are required for the dredging operation, while when the sludge concentration is too high, there could take place deposition of sludge or clogging in the sludge water transfer sytem. Also, it is hard to provide sludge water with controlled sludge concentration in the conventional apparatus, because the screw auger assembly is covered at the upper portion thereof merely by a single piece of hood. Thus, the conventional dredging apparatuses of this type are still open to further improvements.